Vitality, Variation, and Causes of Decline of Trees in Oslo Center (Norway)

To document the health of the most important city trees, a total of 1243 in the Oslo center were surveyed during a five year period. The most frequently planted species in the street environment were Acer platanoides, Aesculus hippocastanum, Tilia platyphyllos, and Tilia x vulgaris. Street trees had poorer health and more severe leaf scorch than park trees. Frequent symptoms of stress on street trees were chlorosis, small chlorotic leaves, necrosis, stem injury, dead twigs and branches, and pest attacks. For some species pests were significantly higher on street trees than in park trees. Tilia platyphyllos and Tilia x vulgaris had the highest ratios among the most commonly planted species. They tolerated the difficult growth conditions along streets surprisingly well, but were often attacked by linden spider-mites which can periodically be a serious problem. Acer platanoides and Acer pseudoplatanus received the lowest ratio and suffered in many cases from severe decline. Aesculus hippocastanum and Betula pendula showed intermediate fitness to street conditions. The most critical factors affecting the tree growth in the Oslo center, were de-icing salt (NaCI), stem injury due to lack of space for tree growth, pest attack, and relatively high soil pH.